In single-ended line tests (i.e. SELT, see, e.g., ITU-T Standard, G.993.2, SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS, Digital sections and digital line system—Access networks, Very high speed digital subscriber line transceivers 2 (VDSL2) (February 2006); ITU-T G.996.2, SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS, Digital sections and digital line system—Access networks, Line Testing for Digital Subscriber lines (DSL); and “Feasibility and problems of DSL loop topology identification via single-ended line tests”, Carine Neus, 16th IMEKO TC4 Symposium Exploring New Frontiers of Instrumentation and Methods for Electrical and Electronic Measurements Sep. 22-24, 2008, Florence, Italy), a known signal is sent over the loop and the reflected signal is analyzed to determine loop characteristics and any impairments present on the line.
Meanwhile, wiring problems within the home and especially close to the customer premises equipment (CPE) are very common. An example is improperly connecting the wire to the CPE. The connector may not have snapped fully either at the CPE or the wall unit, or it could just be oversight in connecting the wire at all. Other reasons could include wiring being disconnected within the home up to the NID. In any event, such connection problems can lead to unnecessary service calls and/or other inconveniences to both the user and the service provider.
In wired communications (such as DSL, cable modem etc.) loop diagnostics are often based on the analysis of single ended loop testing (SELT). However, current SELT techniques by themselves are not sufficiently adept at detecting improper connections such as those described above.